Federal and state governments, along with vehicle manufacturers, test and certify new vehicle emissions, and also carry out some in-use testing of older vehicles. These tests comply with the Federal Test Procedure (FTP) as outlined in the Federal Register, which is a carefully designed and specified three-phase test under "cold transient," "cold stabilized," and "hot transient" conditions. The vehicle is generally driven in a series of accelerations, decelerations, stops, and starts on a chassis dynamometer, whose inertia and friction are specifically set for each vehicle. The emissions from each phase are collected at a constant volume into a sample bag, and the concentrations of each species of pollutant are determined from the integration of the entire bag, with a final result given in grams of pollutant per mile.
The driving course is modeled after a "typical" summertime commute to work in Los Angeles. Each of these tests takes at least twelve hours to complete and costs in excess of about $700, in 1990 dollars. The reproducibility of the results for a given vehicle is believed to be plus or minus 20%, controlled mainly by the repeatability of the vehicle emissions system and not by the test system or gas analysis protocols. Presently available computer models are based on the concept that the FTP emissions measured from a fleet of vehicles are well correlated, although not necessarily one to one, with the emissions that the same fleet would exhibit under in-use driving conditions. However, since very little is known about actual on-the-road fleet emissions, it is impossible to truly gauge the accuracy of this assumption.
In addition to any new car emission certification programs, there are also state inspection and maintenance (IM) programs designed to test every vehicle in a given area that are, therefore, much less rigorous tests. The most sophisticated centralized IM testing programs use a chassis dynamometer with one or two fixed loads and speeds and measure the steady-state emissions as a percentage of the exhaust. Many centralized, and all decentralized, programs measure only idle emissions as a percentage of the exhaust at one, or possibly two, engine speeds.
In late 1986, a fuel efficient automobile test (FEAT) system was developed and designed to remotely detect carbon monoxide and carbon dioxide levels in vehicular emissions and to make specific measurements on individual vehicles. This system is more specifically described in an article entitled "Automobile Carbon Monoxide Emission," Environmental Science Technology, vol. 23, pages 147-149, 1989. Also see "IR Long-Path Photometry: A Remote Sensing Tool for Automobile Emissions," Analytical Chem., vol. 61, pages 671A-676A, 1989. This particular device, while extremely accurate, had its limitations in that it was unable to identify the specific vehicles found to be emitting carbon monoxide in excess of acceptable levels so that the vehicle owner could be subsequently contacted and advised to adjust or repair or modify the vehicle to control its emissions. Moreover, while it was capable of measuring carbon monoxide and carbon dioxide, it was not capable of measuring other emission components or the temperature at which the vehicle was operating, the knowledge of which would be extremely valuable to have.
As indicated, it is known to the inventors that the basic idea of remotely measuring vehicle emissions is not a new one. Lockheed Missiles and Space Corporation first attempted construction of an across-the-road monitor, the successful operation of which was never published. L. Chaney, "The Remote Measurement of Traffic Generated Carbon Monoxide," J. Air Pollution Control Association, vol. 33, pages 220-222, 1983, proved that carbon monoxide fumes (and only carbon monoxide) from passing vehicles could be observed in real-time with a gas filter correlation radiometer. However, Chaney's system did not include any of the parameters required to accurately measure emissions data from vehicle exhaust plume observations.
It would be of particular interest to measure the hydrocarbon emissions as well as nitrogen oxides and water emission levels of identifiable individual vehicles. Therefore, there is still a need for a remote sensing and measuring device to permit measurement of vehicle exhaust while the vehicles are in use. This technique or device permits the quantification of not only carbon monoxide, but also carbon dioxide, hydrocarbons, nitrogen oxides, and water vapor emissions, as well as providing the option of identifying each individual vehicle being tested by the device.